I bought mine at Home Depot. I just called it a "light diffuser" and they knew exactly what I was talking about. They come in 2' x 4' sheets so you'll have to cut them. I spent a ton of time trying to figure out the best way to cut them. We found that a pair of wire strippers snapped them where we wanted them, so try that before tying to cut/saw/whathaveyou. You'll have a lot extra if you are just using it for a clutch or two. I have an entire qt tub tilled with pieces as well as some more in my garage since I bought 2 sheets (I used one for my incubator to act like a shelf on top of my water bottles for my egg box to sit on). I also saw these at Lowes too. I think mine costs about $14 after tax and I have enough for at least 12 egg boxes (I only plan on using 2 this season).